Printer

ABSTRACT

A printer is provided with a plurality of print hammers, each of which is maintained in a rest position engaging a deformed elastic body. Individual magnetic circuits in combination with a single permanent magnet are provided for selectively maintaining each of said print hammers in said rest position and for selectively releasing said print hammers to effect printing. Each magnetic circuit consists of a first portion including a device for adjusting the reluctance of said second portion upon release of the associated print hammer. The first and second portions are connected in parallel with a permanent magnet common to at least two print hammers. Each of said print hammers is released from its rest position by exciting a control coil in said magnetic circuit in a direction such that the magnetomotive force applied to said print hammer to hold said print hammer in position is decreased, the displacement of the print hammer being the product of the release of the energy of the elastic body.

United States Patent [191 Gomi [ PRINTER [75] Inventor: Yoshifumi Gomi,Chino, Japan [73] Assignee: Kabushiki Kaisha Snwa Seikosha,

Tokyo, Japan 22 Filed: Aug, 21, 1973 [21] Appl. No.: 390,289

[30] Foreign Application Priority Data [111 3,834,305 [4 1 Sept. 10,1974 Primary Examiner-Robert E. Pulfrey Assistant Examiner-Edward M.Coven Attorney, Agent, or FirmB1um, Moscovitz, Friedman & Kaplan [57]ABSTRACT A printer is provided with a plurality of print hammers, eachof which is maintained in a'rest position engaging a deformed elasticbody. Individual magnetic circuits in combination with a singlepermanent magnet are provided for selectively maintaining each of saidprint hammers in said rest position and for selectively releasing saidprint hammers to effect printing. Each magnetic circuit consists of afirst portion including a device for adjusting the reluctance of saidsecond portion upon release of the associated print hammer. The firstand second portions are connected in parallel with a permanent magnetcommon to at least two print hammers. Each of said print hammers isreleased from its rest position by exciting a control coil in saidmagnetic circuit in a direction such that the magnetomotive forceapplied to said print hammer v to hold said print hammer in position isdecreased, the

displacement of the print hammer being the product of the release of theenergy of the elastic body.

11 Claims, 3 Drawing Figures Aug. 23, 1972 Japan 47-83641 [52] US. Cl.101/93 C, 335/229 [58] Field of Search B4lj/5/l8; 101/93 C; 5 335/229,230, 235

[56] References Cited UNITED STATES PATENTS 3,628,102 12/1971 Jauch101/93 C 3,659,238 4/1972 Griffing 335/229 3,670,647 6/1972 Funk et a1101/93 C X 3,745,497 7/1973 Cavella 101/93 C X 3,761,850 9/1973Schindler 335/229 MMWMJME PAIENIED SEP 101914 snmwz' PRINTER BACKGROUNDOF THE INVENTION This invention relates generally to a control mechanismfor the print hammers of an on-the-fly printer, and particularly to acontrol mechanism for such print hammers wherein displacement of anyindividual print hammer has no influence upon the operation of any otheradjacent print hammer.

While the use of printers wherein the print hammers are held in a restposition by a permanent magnet and are forced into contact with aprinting surface by a deformed elastic body have taken various forms,embodiments of such printers incorporating a single permanent magnet fora plurality of print hammers have yielded results which are less thancompletely satisfactory. Because the force which is utilized to overcomethe deformed elastic body is the force of a permanent magnet, andbecause it is necessary to reduce the force in order to release thehammer, a change in the reluctance of the portion of the magneticcircuit including the permanent magnet and the print hammer occurs uponthe release of each print hammer. The change in the reluctance of themagnetic circuit affects the operating point of the permanent magnetwhich is used to control a plurality of individual hammers, eachassociated with a separate print column. Normally, the reluctance of thehold portion of the magnetic circuit is increased when the associatedprint hammer is released, thus decreasing the permeance coefficient ofthe permanent magnet. This decrease in the permeance coefficient of thepermanent magnet effects an increase in the magnetomotive force of themagnet at the hammer hold portion of the adjacent columns in which thehammer has not yet been released, hence increasing the force holdingsaid adjacent print hammers at their rest positions, thus altering thecontrol parameters and conditions of said adjacent print hammers. Theforegoing defect is avoided by providing a hammer mechanism wherein theoperating point of the permanent magnet is not changed when a printhammer of one of the print columns is operated.

SUMMARY OF THE INVENTION Generally speaking, in accordance with theinvention, a printer is provided having a plurality of print hammersdisplaceable between a rest position and a printing position, an elasticbody maintained in a deformed state by each of said print hammers at itsrest position, and a magnetic circuit control means for maintaining eachof the print hammers at its rest position and for selectively releasingthe associated print hammer on command. Each said magnetic circuitcontrol means includes a control coil, a first portion including aportion of the print hammer, and a second portion including means forvarying the reluctance of said magnetic circuit control means uponrelease of the associated print hammer. The first and second portions ofeach magnetic circuit control means are connected in parallel with apermanent magnet common to a plurality of said magnetic circuits. Eachmagnetic circuit control means is adapted so that the associated printhammer is normally retained in said rest position by the magnetomotiveforce applied thereto, said magnetomotive force being decreased upon theexcitation of said control coil, said print hammer being displaced fromsaid rest to printing positions by the stored energy of said elasticbody. The variable reluctance means adjusts the reluctance of themagnetic circuit control means so that when said print hammer isreleased from said rest position, the operating point of said permanentmagnet is maintained is substantially the same state as when all hammersare in the rest position.

Accordingly, it is an object of this invention to provide an improvedprinter wherein a hammer is held at a rest position by the magneticforce generated by a permanent magnet while storing energy in an elasticbody such as a spring. I

Another object of the invention is to provide an improved hammer controlmechanism for a printer which maybe actuated by relatively small controlcurrent.

Still another object of the invention is to provide a printer having aplurality of hammers controlled by a common permanent magnet andindividual column circuit control devices wherein the operation of oneof said hammers does not affect the operation of any of the adjacenthammers.

Still another object of the instant invention is to provide a printerhaving a plurality of hammers controlled by a permanent magnet andindividual column magnetic circuit control devices, wherein the releaseof one hammer by altering the magnetic field holding such hammer willhave no influence on the operating point of the permanent magnet. 7

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the constructions hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawings, in which: FIG. 1 is apartially sectioned side elevational view of the operative portion ofone column of a printer including. variable reluctance means constructedin accordance with the instant invention;

FIG. 2 is a side elevational view of a second embodiment of the variablereluctance means constructed in accordance with the instant invention;and

FIG. 3 is a side elevational view of still'another embodiment of anoperative portion of one column of a printer including variablereluctance means constructed in accordance with the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, onecolumn of a multicolumn printer is depicted. The printer includes ahammer I mounted for longitudinal displacement on suspending springs 12.A magnetic circuit for the control of the displacement of the hammer isprovided having a first portion consisting of yokes 2 and 3 havingattractive faces 2a and 3a respectively for holding hammer 1 in a restposition, as illustrated in FIG. 1, by means of the magnetic fieldcaused by the flux from a permanent magnet 4 and depicted as loop i. Asecond portion of said magnetic circuit illustrated by loop ii is formedby permanent magnet 4, a portion of .yoke 2, a control coil 7 3 5awoundabout a yoke 5, gap 11 between attractive face 5b of yoke 5 andattractive plate 6, and is completed by a portion of yoke 3. The rearend of hammer 1 is disposed in Contact with transmitting lever 13,

which lever is pivoted about pivot 20 and which lever further engagesand deforms drive spring 16 when the hammer is in the rest position asillustrated 'in FIG. 1. The drive spring is further supported by areference member such as fixing plate 21. The stroke of transmittinglever 3 is limited by a stopper 15 which is struck by said lever beforethe hammer strikes recording paper 19 and inked ribbon l8 againstprintdrum 17. It is noted that the print energy can be adjusted'by changingthe distance over which the spring force is applied to the hammer bypositioning stopper 15. Reset cam 14 is provided for returning the printhammer and spring to a rest position after the hammer is operated andthe printing is completed by rotating cam 14 against the lower portionof the transmitting lever 13 to thereby deform the spring into the restposition. Printing is effected by engagement of the front end of hammer1 against recording paper 19 to force the recording paper in alignmentwith the-column represented by FIG. 1. In

practice, one such circumferential array of characters would be providedfor each column of the printer. The characters may consist of symbols,numbers or letters as desired.

The; attractive plate 6 is maintained at a distance from the attractiveface 5b of yoke 5 by means of a spring 9 which spring is secured by acap 8 formed of an insulating material. The width of the gap 11 formedbetween attractive face 5a and attractive plate 6 is regulated by a gapadjusting screw which is secured by a stand 7, which stand furtherprovides a surface for pivotally supporting attractive plate 6 betweenstand 7 and yoke 3. i

The operation of the arrangement in accordance with the invention isbest understood by reference to FIG. 1 which is depicted at the restposition of hammer 1. At this position, hammer 1 is held by theattractive faces 2a and 3a of yokes 2 and 3 due to the holding forcegenerated by the magnetic flux loop i which includes the hammer, yokes 2and 3 and permanent magnet 4. The holding force applied to hammer 1 issufficient to overcome the driving force of drive spring 16 and isfurther sufficient to hold the hammer in position despite the influenceof changes in temperature, vibration and the like. As hereinabove noted,a second loop ii is formed, including permanent magnet 4 and isconnected in parallel with the first loop i. The flux in loop 1' is muchsmaller than the flux in loop ii because of the gap 11, permittingeffective use of the permanent magnet within its limited capacity. v i

As noted above,'character-carrying drum 17 rotates at a predeterminedspeed. When the selected character approaches alignment with hammer 1, asignal is applied to control coil 5a. The direction of the signal ap-'plied to control coil 5a is such as to increase the quantity of magneticflux flowing in magnetic flux loop'ii.

the character on the print drum by the spring and continues to besupplied with energy until the transmitting lever 13 is brought intocontact with stopper 15. As the print hammer strikes against thecharacter drum the printing function is performed. The print hammerrebounds off the print drum to return to the rest position,

spring 16 being returned to the rest position by reset cam 14.

. As has been pointed out above the printer illustrated in FIG. 1represents only one column of a line printer. The printer includes aplurality of columns each including a print hammer. Although each hammerhas a separate magnetic circuit for that column, the magnetic circuitsof all or a portion of the columns share the use of the same permanentmagnet 4. Thus, when one such hammer is released in the mannerhereinabove discussed, the reluctance of the associated magnetic circuitincluding the permanent magnet is changed, altering the operating pointof the permanent magnet. Alteration of the operating point of thepermanent magnet affects the other columns which have hammer magneticcircuits cooperating with the same permanent magnet, the hammers ofwhich have not yet been released from their respective hammer holdpositions. The alteration in the operating point of the permanent magnetincreases the amount of magnetic flux flowing through the hammer holdportion of the magnetic circuits of the adjacent columns which have notyet been released. This increase in the amount of flux in the adjacentcolumns causes an'increase in the force of loop i in the other columnsand a stronger signal must then be applied to the control coils of theadjacent columns in order to allow the hammers of such adjacent columnsto be released. Moreover, even if the power is sufficient to release thehammer of the adjacent columns an increased time is required to supplythe current needed for releasing such adjacent hammers. Variations inthe time between the application of a print command and the release ofthe associated hammer depending on whether another hammer has previouslybeen released results in a reduction in printing quality.

The above-mentioned defects are eliminated in the instant invention byproviding a variable reluctance means as part of magnetic flux loop ii.When the print hammer is released from the hammer hold position suchrelease is effected by an increase in the flux in loop ii by theapplication of a signal to control coil 5a. The increase of flux in loopii causes attractive plate 6 to be attracted closer to attractive face5b, thus narrowing the gap 11 therebetween. As the print hammer isreleased from the hammer hold portion and is moved toward the character,most of the magnetic flux generated by permanent magnet 4 flows intoloop ii. Because of the deflection of the attractive plate 6 towardsattractive face 5b, the reluctance seen by the permanent magnet 4remains constant and the operating point of the permanent magnet ismaintained substantially constant regardless of the position of theprint hammer. Accordingly, the print hammers can be controlled with aminimum of electric power and the time between print command and thestriking of the hammer against the character is maintained constant forall of the hammers regardless of the conditions of the other columns sothat printing quality is enhanced.

Reference is now made to FIG. 2 wherein means are provided for adjustingthe variable reluctance means to provide precise adjustment thereof.Like reference numerals are used to denote like elements illustrated inFIG. 1. A stand 27, formed of a non-magnetic material, is provided forgap adjusting screw which stand includes a stopperportion 27a foradjusting the minimum gap between the attractive plate 6 and theattractive face 5b when the attractive plate 6 is attracted to saidattractive face during application of a print command signal. Adjustingscrew 10 is included for selecting the width of the gap 1 1 during theperiod whenthe hammer is in the rest position. The minimum width of thegap 11 when the attractive plate 6 is moved toward control coil 5 duringmovement of the hammer is adjusted by means of screw 28. The stopperportion 27a of stand 27 is moved in the direction of arrow A about apivot defined by thinned portion 27b of stand 27. Accordingly, byselecting the gap width at the time when the print hammer is releasedfrom the hammer hold position and the attractive plate 6 is attracted tothe attractive face 5b, it is possible to adjust the reluctance of thehammer magnetic circuit defined by loop ii so that the reluctance seenby the permanent'magnet remains essentially constant before and afterrelease of the print hammer, thus maintaining constant the operatingpoint of permanent magnet 4.

Reference is now made to FIG. 3 wherein like reference numerals are usedto denote like elements. In FIG. 3, the two parallel magnetic loops aredefined, but the control signal supplied to coil 5a is supplied in loopi to decrease the flux of loop 1' by applying a magnetic field in adirection opposite to that produced bythe permanent magnet. As isappreciated by the skilled artisan, by use of the variable reluctancemeans hereinabove described the same beneficial effect is achieved andpermanent magnet 4 is maintained at a substantially constant operatingpoint.

As is understood, a printer constructed in accordance with the instantinvention wherein the print hammer is supplied with energy of a deformedelastic body according to a print command, is operated so that theactuation of one print column does not influence any other columns. Thusprint hammers can be controlled by the use of very small amounts ofelectric power to thus realize stable action of the hammers without thenecessity of supplying complicated controls.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above constructions withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained inthe above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. Y

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and-all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:

l. A printer comprising at least two print hammers each displaceablebetween a rest and a print position; an elastic body maintained in adeformed position by each of said print hammers at its respective restposition; and magnetic circuit control means for holding each saidhammer at said rest position and releasing same for selectivedisplacement to said print position by the energy of said deformedelastic body, including a permanent magnet common to at least two ofsaid print hammers for producing the magnetomotive force for holdingsaid print hammers at their rest positions, a portion of each of saidprint hammers forming a part of the associated magnetic circuit controlmeans when at their rest positions, a control coil associated with eachprint hammer and positioned so that the magnetomotive force applied tosaid print hammer is decreased upon the application of a signal to theassociated control coil to release said print hammer to effect printing,and means for varying the reluctance of each of said magnetic circuitcontrol means upon the release of the associated print hammer tomaintain the operating point of said permanent magnet substantiallyconstant before and after the release of said associated print hammerfrom its rest position.

2. A printer as recited in claim 1, wherein each said magnetic circuitcontrol means includes a first portion including said portion of saidprint hammer and a second portion including said variable reluctancemeans, said first and second portions being connected in parallel withsaid permanent magnet and each other.

3. A printer as recited in claim 2, wherein said variable reluctancemeans includes means defining a gap in said second portion and meansresponsive to the magnetomotive force generated by the application ofsaid signal to said control coil for adjusting the width of said gap soas to narrow said gap upon the release of the associated print hammer.

4. A printer as recited in claim 3, wherein said variable reluctancemeans includes a fixed magnetic circuit member magnetically coupled tosaid control coil and defining an attractive face and an attractiveplate mounted for displacement toward and away from said attractive faceto define said gap, said attractive plate being displaced toward saidattractive face in response to the magnetomotive force of said controlcoil.

5. A printer as recited in claim 4, wherein said variable reluctancemeans includes means for biasing said attractive plate in a positiondefining a maximum gap width.

6. A printer as recited in claim 5, wherein said variable reluctancemeans includes means for selectively setting said maximum gap width.

7. A printer as recited in claim 6, wherein said attractive plate ispivotally mounted, said means for selectively setting said maximum gapbeing a setting screw.

able reluctance means includes stopper means in the path of saidattractive plate toward said attractive face todefine a minimum gapwidth.

11. A printer as recited in claim 10, wherein said variable reluctancemeans includes means for selectively positioning said stopper means toset said minimum gap width.

1. A printer comprising at least two print hammers each displaceablebetween a rest and a print position; an elastic body maintained in adeformed position by each of said print hammers at its respective restposition; and magnetic circuit control means for holding each saidhammer at said rest position and releasing same for selectivedisplacement to said print position by the energy of said deformedelastic body, including a permanent magnet common to at least two ofsaid print hammers for producing the magnetomotive force for holdingsaid print hammers at their rest positions, a portion of each of saidprint hammers forming a part of the associated magnetic circuit controlmeans when at their rest positions, a control coil associated with eachprint hammer and positioned so that the magnetomotive force applied tosaid print hammer is decreased upon the application of a signal to theassociated control coil to release said print hammer to effect printing,and means for varying the reluctance of each of said magnetic circuitcontrol means upon the release of the associated print hammer tomaintain the operating point of said permanent magnet substantiallyconstant before and after the release of said associated print hammerfrom its rest position.
 2. A printer as recited in claim 1, wherein eachsaid magnetic circuit control means includes a first portion includingsaid portion of said print hammer and a second portion including saidvariable reluctance means, said first and second portions beingconnected in parallel with said permanent magnet and each other.
 3. Aprinter as recited in claim 2, wherein said variaBle reluctance meansincludes means defining a gap in said second portion and meansresponsive to the magnetomotive force generated by the application ofsaid signal to said control coil for adjusting the width of said gap soas to narrow said gap upon the release of the associated print hammer.4. A printer as recited in claim 3, wherein said variable reluctancemeans includes a fixed magnetic circuit member magnetically coupled tosaid control coil and defining an attractive face and an attractiveplate mounted for displacement toward and away from said attractive faceto define said gap, said attractive plate being displaced toward saidattractive face in response to the magnetomotive force of said controlcoil.
 5. A printer as recited in claim 4, wherein said variablereluctance means includes means for biasing said attractive plate in aposition defining a maximum gap width.
 6. A printer as recited in claim5, wherein said variable reluctance means includes means for selectivelysetting said maximum gap width.
 7. A printer as recited in claim 6,wherein said attractive plate is pivotally mounted, said means forselectively setting said maximum gap being a setting screw.
 8. A printeras recited in claim 6, wherein said variable reluctance means includesstopper means in the path of said attractive plate toward saidattractive face to define a minimum gap width.
 9. A printer as recitedin claim 8, wherein said variable reluctance means includes means forselectively positioning said stopper means to set said minimum gapwidth.
 10. A printer as recited in claim 4, wherein said variablereluctance means includes stopper means in the path of said attractiveplate toward said attractive face to define a minimum gap width.
 11. Aprinter as recited in claim 10, wherein said variable reluctance meansincludes means for selectively positioning said stopper means to setsaid minimum gap width.